Direct drive/rim drive/idler drive vs. belt drive?

Albert,

I may get into trouble here, but I am increasingly convinced that the micro-dynamics of analog playback, in particular, hinge partly on things we have yet to measure. I thought I had built a great turntable, but somehow I inadvertently improved the dynamics of it without trying by implementing a change to make assembly easier. We may have figured out a lot about audio, but I really believe there are still volumes left out there for us to discover. I suppose the goal should be not to know everything, but to not know as little as the competition...assuming it is about competition, and I'm not so sure that that should be the end goal. Me? I'll settle for good sounding no matter where it originates. :)

Albert that's not strange at all when you look at the way Technics implemented their servo drives.

They drive the motor coils with single ended amplifiers using capacitive coupling to block the inevitable DC offset. Any such amplifier is very sensitive to the quality of the coupling cap used because it is in series with the motor coil. If the impedance of the cap increases, as it inevitably will with age, the drive available to the motor drops which will in turn reduce the forward slew rate.

I agree that there are a lot of things going on with the various drive mechanisms. Where we might disagree is with your implication that this means they cannot be adequately analysed. The reason I was dismissive of the parts per million difference due to belt stretch is that the belt creep is around 1000 times larger, so there's no point in worrying about belt stretch - by the time you fix the creep problem the stretch problem is gone as well.

Mark Kelly

I was thinking about the SL1200 series - the SP10s used push pull pairs on a dual rail power supply. Since there is no coupling capacitor it can't be the problem but it is still the case that the amplifier will be sensitive to the quality of its power supply.

I'm not an engineer,but more mass seems like it would sound better on all drive systems as long as its done right.That will put more load on the bearing too.The softer the rubber used for the idler or drive belt will probably make it more quiet also resulting in a nicer table.One thing we must keep in mind is good maintenance.About 35 years ago,I had a nice turntable that was pricey for me. The belt got loose from age,so I took it to a mid to high end dealer to let them change it.I thought I was hearing something that wasn't right.By the time I looked into it,the motor bearing was destroyed from the junk tight rubber band belt the dealer used.Try to learn about your table to keep an eye on things.

Hifitime
y.s.: >>>...the motor bearing was destroyed from the junk tight rubber band belt the dealer used<<<

Now what 'table would that have been, I ask?

To get a belt THAT tight, the motor if it was out-board would simply fall over, or?

BUT, if not out-board --- well that's another story. So before I go on, can we hear about this tt by any chance.
Thanks,